Ion Temperature-Gradient-Driven Modes in Tokamaks and Stellarators T. Rafiq , M. H. Nasim and M. Persson Department of Electromagnetics and Euratom/VR Association, Chalmers University of Technology, S-41296 Gothenburg, Sweden Abstract The influence of plasma geometry on linear stability of ion temperature-gradient- driven drift modes is investigated in the H1-NF and W7-X stellarators and the results are compared and contrasted with those of a JET like tokamak equilibria. The results of the JET-like equilibrium are also compared and contrasted with the results of a circular equilibrium with the same aspect ratio. In stellarators unstable modes are found both in good and bad curvature regions, while in tokamaks, these are found only in the bad curvature region however, growth rate is found small in W7-X as compared to other geometries considered. The magnetic field configuration and eigenvalue equation Modern stellarators are designed with neoclassical transport in mind, potentially leading to anomalous transport originating from drift wave turbulence as the primary cause of energy and particle losses. It is therefore of interest to consider the influence of details in the geometry on drift wave stability. The objective of the present paper is to study the ion temperature gradient (ITG) driven drift instabilities in different stellarator and tokamak configurations with the purpose to contribute to the understanding of the geometrical effects on these instabilities. A three field periods heliac (H1-NF), a five field period helias (W7-X), circular and noncircular tokamaks are selected to study the effect of geometrical properties such as local magnetic shear, normal curvature, geodesic curvature and magnetic field. The VMEC code is used to obtain the 3-D equilibria. The magnetic field can be expressed in terms of the Boozer coordinates (s, θ, ζ ) as B = ∇α × ∇ψ = ˙ ψ∇α × ∇s, with ˙ ψ ≡ dψ/ds = B o ¯ a 2 /2q where α = ζ - qθ is the field line label, ζ is the generalized toroidal angle, θ is the generalized poloidal angle, q is the safety factor, s =2πψ/ψ p is the normalized poloidal flux and serves as the radial coordinate. Here 2πψ is the poloidal magnetic flux bounded by the magnetic axis and ψ = constant surface, ψ p = πB o ¯ a 2 /q is the total poloidal magnetic flux, where B o is 30th EPS Conference on Contr. Fusion and Plasma Phys., St. Petersburg, 7-11 July 2003 ECA Vol. 27A, P-3.9